Working magnesium



Patented Aug. 3, 192 6.

. UNITED STATES PATENT: OFFICE.

HERMAN E. BAKKEN, OF NIAGARA FALLS, NEV YORK, ASSIGNOR TO AMERICAN MAG-NESIUM CORPORATION, OF NIAGARA FALLS, NEW YORK, A CORPORATION OF NEWYORK.

WORKING MAGNESIUM.

No Drawing. Original application flle d November 1, 1922,'Seria1 No.598,292. Divided and this application filed December 31, 1-824.- SerialNo. 759,146.

My invention relates to the production of formed shapes of metallicmagnesium. "The invention is based upon my discovery of a novel methodwhereby loose or loosely 5 coherent masses of crystallized magnesium canbe consolidated and formed into structurally sound and commerciallyuseful shapes.

In the processes that have heretofore been employed for utilizing themagnesium as obtained from the electrolytic reduction process, it hasbeen necessary at some stage to handle the metal in molten form.Magnesium is exceedingly active'chemically and at temperatures slightlyabove its melting point, 651 (3., will combine with both oxygen andnitrogen of the air. In fact, it is very difficult, even with the mostcareful melting, to prevent burning at the surface 2 of moltenmagnesium. The non-metallic impurities introduced in this way exert amarked influence on the physical and chemical properties of the metalwhen present in only a very limited degree.

In my co-pending application, Serial No. 598,292, filed November 1,1922, and of which this application is a division, I have disclosed aprocess of producing sublimed magnesium in a crystallized form andsubstantially free from'non-metallic inclusions. Briefly, the inventionthere disclosed con sists in placing in one end of aclosed retort, crudemetallic magnesium or magnesium scrap, such as castings, alloys, etc.,and then heating the said metal at a temperature of about 300 to 651 C.for a suitable pe riod, say, 5 to 6 hours, while maintaining M anabsolute pressure of 0.5 to 0.2 mm. of mercury in the retort. Under suchconditions, the magnesium will rapidly sublime and condense in thecooler end of the retort in the form of a loosely cohering mass ofaggregated crystals When the sublimation is completed and the apparatuscooled somewhat the crystallized masses can be removed in a suitablemanner. the crystals of magnesium made in this way has shown amagnesium. content as high as 99.989%. The crystallized 'mass will showfully developed, bright metallic crystal faces of magnesium. Thecrystals vary in size and some may have crystal faces as large, asone-fourth of a square inch in area Analysis of or more. Being coherent,the masses can be readily handled, but since they are only looselycoherent, they can be readily broken' into pieces of suitable size forfuture use.

In using the term crystallized magnesium, l have reference to a productproduced by a process wherein the'crystals are free, at least in part,to grow and assume their'typical external shape.

Magnesium which has solidifiedfrom the liquid state is crystalline, ofcourse, but not crystallized in the sense here employed. It is composedof closely coherent grams having an internal crystalline structure butwhich when forming were not free to grow and assume their typicalexternal shape.

Crystal metal as produced by my process can be made exceedingly pure. Byvirtue of the absence of reactive agents, such as nitrogen and oxygen,the crystallized mass is substantially free from inclusions of ox- Iides and nitrides. In certain cases where the crude..or scrap magnesiumwhich is to be sublimed contains zinc or other relatively volatilemetal, some of this metal may be found alloyed in the sublimed crystals.In some cases this alloying may be ermissible 30 or even desirable andthe crysta masses so obtained may be employed in my present process justas are the crystalline aggregates of pure magnesium, since they aresubstantially free from non-metallic impurities. ea In general, however,where the hardness of the. crystals has been increased by alloying,higher pressure will be required. If only prior methods were availablefor working this new product into useful shapes, then much of theadvantage of its high purity would-be sacrificed during the neces sarymelting process. I have discovered, however, that mycrystallizedmagnesium is sufiiciently plastic and free from impurities,so that under suitable conditions of temperature and pressure thecrystals will flow and weld together'into a structurally sound metalbody. Loose fragments of suitable size can be placediwthe chamber of anex- 1 trusion press, for example, and expressed directly through the dieopening into any of the customary structural sha es, such as wire, bars,tubes, rods, etc. T e best re- 1 sults will be obtained when the metalis extruded within a temperature range of about) r 300 to 4.25 C. Ingeneral, it will be found desirable to employ a high extrusion pressurein order to more perfectly weld the crystal fragments together.

In order to obtain sufficient pressure within the preferred temperaturerange and also in order to obtain a smooth surface on the extrudedproduct, I have found it desirable to effect a high reduction from 'thecrosssectional area of the extrusion cylinder to that of the extrudedproduct. This reduction should be preferably about 99% or higher.

I have extruded crystallized magnesium from a 3 inch diameter cylinderinto wire 30 mils in diameterat a temperature of about 375 C. and apressure of about 80,000 pounds per square inch. This wire had a smoothsurface, a tensile strength of about 35,000 pounds per square inch andan elongation of about 3% in 2 inches. These properties are as good asthough the wire was extruded under the same conditions of temperatureand pressure from the cast billet.

Other methods of consolidating the crystalaggregates may be employed.For example: The crystals can be compressed into briquets or other formsat a temperature of about 200 C. or higher to give a substantiallychemically pure metal in a marketable form. Since my process avoidsmelting, the product is substantially as free from oxides, nitrides andother impurities as the crystallized metal from which it is produced. Myprocess is also economical since it eliminates the large losses usuallyunavoidable in the melting and casting of magnesium.

By'the term magnesium, I comprehend not only the metal itself, butalsosuch alloys of magnesium as have substantially the same physicalproperties as the metal and there- -fore lend themselves to the sametreatment.

. pressure as will cause the crystals to flow together and unite in astrongly coherent product.

2. A method of die-expressing ma 'nesium into commercial form,comprising subjecting melting point of the metal to such pressure aswill cause the said aggregates to flow to gether and form a metallicbody having substantial strength.

4. A method of plastically working magnesium into commercial formscomprising subjecting particles of magnesium substan-. tially free fromnon-metallic inclusions and at a temperature below the melting point ofthe metal tosuch pressure as will cause the particles to flow togetherand form a metallic body having substantial strength.

5. A method of die-expressing magnesium into commercial forms comprisingsubjecting crystallized magnesium in a pressure chamber while at atemperature below its melting point to such pressure as will cause thecrystallized particles to unite and plastically flow out of the chamberthrough an aperture.

6. A method of producing structurally sound forms from crystallizedparticles of magnesium produced by sublimation, comprisingdie-expressing said particles from a pressure cham er, the ratioof-cross-sectional area of this chamber to that of the die opening beingso adjusted that a reduction in excess of about 99% is effected.-

7 A form-ed shape of structurally sound metallic magnesium, havingsubstantial strength and ductility, and composed of plastically deformedand strongly coherent pressure welded crystals of sublimed magnesium. I

8. A formed shape of metallic magnesium, substantially free frominclusions of oxides and nitrides and composed of plastically deformedand pressure welded crystals of sublimed magnesium.

In testimony whereof I afiix my signature.

HERMAN E. BAKKEN.

